Stratospheric Ozone (O 3 ) Formation and Depletion History of problem and solution Tie to Climate Change

The Ozone layer Diffuse layer containing ozone (O 3 ) molecules Reacts with UV light from the sun Blocks some UV that causes skin cancer where layer is thick

Stratospheric Ozone Formation In the mid-stratosphere over the tropics ozone (O 3 ) is created: 1. Oxygen is split by UV light 2.Ozone formation 3.Ozone absorbs UV light and is decomposed, protecting us

The Ozone Hole “Stratospheric ozone depletion” Sources – Anthropogenic (“human-caused”: compounds containing Chlorine, such as Chlorofluorocarbons (CFCs)) – Natural depletion at a rate equal to rate ozone is created Former uses of chlorine-containing compounds: solvents to clean computer circuit boards, coolants in air conditioners & refrigerators, fire extinguishers, aerosol cans, styrofoam

Natural Ozone Depletion Ozone photolysis – degradation by sunlight Normally in equilibrium with ozone formation

Anthropogenic Ozone Depletion Chlorine-containing compounds released into the atmosphere react with ozone Chlorofluorocarbons (CFCs) ex: freon Cl + O 3 ClO + O 2 ClO + OCl + O 2 net:O + O 3 2O 2 ozone destruction

More on the ozone hole CFCs (like freon) are stable near Earth’s surface at lower atmospheric and thus can make it up to stratosphere In the upper atmosphere, CFCs decompose to Cl (chlorine radicals) One Cl atom can break down 100,000 Ozone (0 3 ) molecules Poles and high altitudes most affected - O 3 cannot form at the poles

Impacts of Ozone Hole Harm to human health: More skin cancers, sunburns and premature aging of the skin. More cataracts, blindness and other eye diseases. Adverse impacts on agriculture, forestry and natural ecosystems: Reduced growth, photosynthesis and flowering Damage to marine life: Plankton are threatened by increased UVB radiation. -Plankton are the first vital step in aquatic food chains. Animals: May cause eye and skin cancers. Can harm marine animals in their developmental stage (e.g. young fish, shrimp larvae and crab larvae)

History of Finding Problem and Fixing 1974-Sherwood Rowland and Mario Molina predict CFCs will break down stratospheric ozone. (Later won Nobel Prize) 1976-UN calls for an international conference 1981 UN creates global convention to protect ozone 1985-Hole in ozone discovered over Antarctic (7.3 million square miles) countries sign Montreal Protocol to reduce and eliminate Chlorine containing compounds 1990s-peak of ozone depleting compounds in atmosphere

Benefits of Montreal Protocol By 2165, actions to protect and restore the ozone layer will prevent an estimated 6.3 million U.S. deaths from skin cancer. By 2165, protecting stratospheric ozone layer will produce an estimated $4.2 trillion in societal health benefit in the U.S. The ozone layer has not grown thinner since 1998 over most of the world and it appears to be recovering. Antartic ozone is projected to return to pre-1980 levels by 2060 to EPA (2007)

Is Ozone Hole related to Climate Change? Process of replacing CFCs created more energy efficient appliances (refrigerators)-decreasing greenhouse gases (GHGs) Climate change may slow Ozone recovery Many ozone-depleting substances are also potent GHGs – thus the decrease in amount of CFCs has been positive for climate change